As demand increases for smaller micro-manufactured parts in the rapidly growing fields of optics, automotive, and medical devices, the impact of burrs within these parts also increases. As generally referred to herein, a burr may be a small piece of material or raised edge that remains attached to a workpiece after machining. A burr may be a fine wire or a projection or raised portion of the surface. The process of removing these unwanted burrs is usually referred to as deburring.
Burrs cause many problems in assembly and operation. Protruding burrs can cause, among other things, electrical shorts, air leaks, jammed mechanisms, increased wear and stress, turbulence and non-laminar liquid and air flow. A burr can physically harm assemblers or end-users. As the size of parts becomes smaller, the size of burrs is reduced; however, the burr-to-feature size ratio increases and thus, conventional deburring processes begin to cause significant surface damage. JOURNAL OF MATERIALS PROCESSING TECHNOLOGY; vol. 209, issue 1; 19 Jul. 2009; pp 5399-5406; “Deburring microfeatures using micro-EDM”; Jeong, et al.
Various machining methods are used to manufacture micro-parts, e.g. parts that are either sub-millimeter in size or include sub-millimeter sized features. Conventional processes such as physical cutting, milling, drilling, turning, etc., inevitably leave behind small bits of material due to the plasticity of the material at the cutting tool interface. Recast burrs are the result of solidification or redeposition of material on the surface, resulting from, for instance, an EDM process. Even though new machining systems reduce the cost of manufacturing micro-parts and features, much of these savings are offset by outdated deburring methods.
Deburring has always been an afterthought in the effort to control manufacturing costs. A company may initially invest hundreds of thousands, even millions, of dollars on a manufacturing center, but give little strategic thought to how to deburr and finish the part. There are still companies employing high paid technicians looking through microscopes removing microburrs from individual pieces with small blades, files and lapping compounds. Each feature can require several minutes of deburring time. This repetitive process exposes employees to stress injuries and their employers to additional liability.
There are currently available various methods of removing burrs on micro-parts and features. These processes include electrochemical polishing, abrasive finishing, thermal deburring and ultrasonic machining, among others by hand. Though all of these methods matured with machining technologies, each of them has its shortcomings.
Current deburring processes can damage or over-machine the surface, change the dimensions of the part, blunt sharp edges, break the edge (which may not be desirable) or require additional cleaning processes to remove etching residues. In many cases, micro-parts and features are actually getting smaller than the tools and media used to deburr them. Within the medical industry and its continued miniaturization of products, removing burrs while maintaining precision tolerances is not just a matter of quality, it is a greater matter of health and safety.
Generally, deburring is considered a secondary process. Even though this manufacturing step has been around since the invention of steel, it still receives little attention in the initial budgeting of product manufacturing and marketing. However, as an afterthought, it can add a substantial cost on the back end of manufacturing a product.
There are currently many approaches to deburring micro-machined parts. Product managers must determine the proper deburring process based on numerous variables, including material, part size, feature size and intricacy.
In some instances, deburring is already processed on the same platform used to manufacture the workpiece or part, but with extensive tooling changes required. In other instances, the parts are removed from the machining platform and deburred in third party CNC (computer numerical controlled) machines with either lasers or high pressure abrasive jets. In many cases workpieces are so intricate that they are deburred by hand with micro-files and tools under a microscope. Each of these processes suffers the significant shortcoming of requiring removal of the part from the original manufacturing tools and tooling by one or more degrees.
Swapping tools within the same platform is currently the most organic deburring process of the group. There are commercially available macro tooling and polishing brushes that are chucked into conventional machine tools to remove burrs in a full contact process. Although these are the most organic processes, these types of deburring tools must deal with referencing and calibration issues for tool run-out and have a comparatively high chance of damaging the part and changing its dimensional characteristics and precision. This method is not being applied to micro features and micro parts due to the large size of the deburring tools.
Another deburring method is to remove the part from the platform and fixture it onto an auxiliary CNC machine tool specifically for deburring. This method adds additional steps and referencing to the process, greatly increasing the difficulties of precision removal of burrs. Also commercially available are abrasive flow machines that use a high pressure (>50 MPa) jet of abrasive media to deburr and finish parts. Laser deburring techniques are also employed in some manufacturing companies.
There is a demand, therefore, for a platform portable deburring system that does not require extensive tooling changes or cleaning of the part after the deburring process. Such a deburring system can be mounted on the machine tool used to form the workpiece. This will reduce costs by increasing efficiencies when compared with existing processes as well as eliminating calibration and referencing inaccuracies inherent in moving the workpiece from one machine to another.
There is also a demand for a platform portable deburring system that imparts no mechanical force to the part being deburred.
There is demand also for a platform portable deburring system tailored for microparts that leaves crater sizes of less than 100 nm, resulting in a virtually damage-free surface with little evidence of the previous burr or the deburring process on the final part.
Micro-electrical discharge machining (μEDM) is uniquely suited to remove unwanted burrs from micro (defined as sub-millimeter-sized) parts and micro features of larger parts. It is a localized non-contact process and will not affect the general surface finish features or dimensions of pre-machined parts.